This invention relates to disc type chippers for cutting substantially uniform chips from a log. The invention is more particularly concerned with structure on a chipper to limit the size of slivers that can form on the bedknife side of the log as it is fed into the chipper.
A chipper of this general type is described, e.g., in U.S. Pat. No. 4,784,337, which depicts a large vertical disc type chipper of the Carthage-Norman design. These chippers have a vertically disposed disc that rotates about a horizontal drive shaft mounted on a suitable base or mount, and is driven by a large electric motor. The disc is enclosed in a protective cover. Logs are introduced through a feed spout or chute into a port or opening in the cover, and contacted against the disc. In an over-shaft design, the spout or feed chute passes through an upper part of the hood portion of the cover. In an under-shaft design the spout is disposed below the shaft and introduces the logs to the cutting disc at a position beneath the shaft.
In all of these disc-type chippers, the disc has a series of generally, but not necessarily, radial cutting stations in each of which a blade assembly is positioned alongside a chip slot that passes through the disc from a proximal or feed side to a distal or discharge side. The knife assemblies are disposed with cutting edges oriented at a predetermined angle from the proximal face of the disc and the cutting edges lie in a cutting plane.
At the feed chute or spout, the rotary disc sweeps the cutting blade assemblies across the feed port in one direction, i.e., from a leading side to a trailing side. At the trailing side of the port there is a stationary bedknife. The bedknife is supported on a front frame of the machine and is housed in the cover. The trailing side of the log in the spout is positioned against the bed knife. As the disc rotates, the cutting knife assemblies are moved past the bedknife at high speed. The cutting blade assemblies rapidly cut chips from the face of the log. The chips then pass through the chip slot and are discharged at the distal side of the disc.
The bedknife has a support surface with a distal edge positioned, at least initially, a predetermined small clearance from the cutting plane of the disc knife assemblies. In operation the knifes will wear down progressively which opens the clearance somewhat.
At this position where the log is against the bedknife these chippers have a tendency to strip off a long sliver. Because the wood in the log is somewhat green and has a significant moisture content, the knife assemblies tend to flex the wood enough to bend between the disc and the bedknife. This forms the sliver which then proceeds generally horizontally between the disc and the bed knife. If unchecked, the sliver can continue for the entire length of the log, which can be a distance of twenty feet or more. The problem of slivers worsens as the clearance between the stationary bedknife and the rotary knives becomes large. These slivers, which are thin fillets of green wood ripped in the grain direction from the logs, often become balled-up and can clog the chipping machinery or associated size screening equipment.
However, to date there has been no effective means offered which prevents slivers or limits their size.